The present invention is directed generally toward coal preparation plants and, more particularly, toward an improved integrally formed magnetic separator and screen feedbox assembly for receiving and mixing with water, raw coal particles received at a coal preparation plant.
Coal preparation plants separate organic and non-organic solid particles by their specific gravities. The coal preparation plant receives a feed of raw mined coal and separates the raw mined coal into clean coal and refuse. Coal preparation plants typically utilize two basic processing methods for separating raw coal from rock and varying proportions of striated rock and coal from the higher quality coal. These two processing methods include heavy media and water based separation methods. Heavy media, utilizing a slurry of media, e.g., water and magnetite or ferrosilicon, to separate the coal from the refuse according to their specific gravity of dry solids, is the most common separation process for larger size (Plus 1 mm-0.5 mm) particles. Whereas, water based separation processes are more commonly used for the xe2x80x9ccleaningxe2x80x9d of the finer sized particles, as that term is commonly understood in the coal preparation art. One type of heavy media circuitry used in the coal preparation plants includes a heavy media cyclone.
Coal preparation plants using heavy media cyclones operate with three separate types of screens for coal processing, namely, a deslime screen, a refuse screen and a clean coal screen. A common screening assembly used in many coal preparation plants today known as a vibratory banana screen. The deslime screen receives the raw coal feed particles and separates them into coarse and fine sized fractions. The coarse or larger sized particles discharged from the deslime screen surface are directed to the heavy media separation section of the coal preparation plant, while the finer sized particles passing through the deslime screen are directed toward the water based separation section of the coal preparation plant.
The clean coal and refuse screens receive the clean coal and refuse particles, respectively produced by the heavy media separating section. While on the clean coal and refuse screens, the clean coal and refuse particles are rinsed with water, and the finer particles and water passing through the respective screens are recirculated through the coal preparation plant. Rinsing the clean coal and refuse particles is primarily done to recover the particles of media, such as magnetite, remaining thereon as a result of the coal/refuse separation process, as magnetite can be quite expensive.
Typically, the slurry of magnetite and water recovered by the underpans of the clean coal and refuse screens are either pumped or gravity fed to a magnetic separator for magnetite recovery. The slurry of magnetite and water is passed through the magnetic separator which recovers the magnetite from the slurry and returns the magnetite to the heavy media processing section of the coal preparation plant. The remaining water from which the magnetite has been removed, often called tailings water, is discharged by the magnetic separator and reused as process water by the coal preparation plant.
In a coal preparation plant which receives a raw coal feed and separates the raw coal feed into a clean coal and a refuse, an apparatus is provided for use therein. The inventive apparatus receives and mixes the raw coal feed with water. A feedbox receives the raw coal feed and directs the raw coal onto a deslime screen for separation into coarse and fine sized raw coal fractions. A magnetic separator, and specifically the magnetic separator tank, is provided which is integrally formed with the feedbox. The magnetic separator receives an input slurry of magnetic solid particles and water from the coal preparation plant, and separates the magnetic solid particles from the input slurry. The overflow tailings slurry output by the magnetic separator from which magnetic solid particles have been removed is received directly by the feedbox and mixed with the raw coal feed particles received thereby.
In one form, the overflow tailings water output by the magnetic separator is received by the feedbox across an entire width thereof.
The magnetic separator typically includes a feed chamber receiving the input slurry of magnetic solid particles and water and an outlet discharging the overflow tailings slurry. In another form of the present invention, the overflow tailings outlet is integrally formed with the feedbox such that the overflow tailings slurry output thereby is received directly by the feedbox and mixed with the raw coal feed received by the feedbox. In a preferred form, the overflow tailings outlet includes an overflow weir extending the full width of the feedbox.
The magnetic separator also typically includes an underflow tailings outlet formed in the bottom surface thereof for discharging an underflow tailings slurry. Typically, the misplaced coarser sized material settling on the bottom surface of the magnetic separator is included in the underflow tailings slurry and is output at the underflow tailings outlet directly onto the deslime screen or piped to a separate location.
The magnetic separator may include a counter current rotating drum type magnetic separator having a bottom surface and end walls defining a chamber for retaining the input slurry of magnetic solid particles and water. A rotatable drum is provided having a cylindrical wall with a portion positioned beneath a surface of the slurry retained in the process chamber and a magnet positioned within the rotatable drum in proximity to the cylindrical wall and extending around at least the portion of the cylindrical wall beneath the slurry surface. The slurry inlet is positioned on a first side of the bottom surface for feeding the input slurry of magnetic solid particles and water to the process chamber. The concentrated magnetic solid particle outlet is positioned on the first side of the bottom surface for outputting the separated magnetic solid particles. The overflow weir, is positioned on a second side of the bottom surface opposite the first side and outputs the overflow tailings slurry from which magnetic solid particles have been removed via magnetic attraction to the drum. The overflow tailings slurry is received directly by the feedbox mixing with the raw coal feed received therein.
In a further form, the feedbox further includes a coal retention area xe2x80x9cdrop boxxe2x80x9d where the raw coal feed received by the feedbox is mixed with the overflow tailings slurry output at the overflow weir.
A method according to the present invention is also provided for mixing a raw coal feed received at a coal preparation plant with water. The inventive method generally includes the steps of receiving a raw coal feed at a feedbox of a receiving assembly in the coal preparation plant, providing a magnetic separator integrally formed with the feedbox of the receiving assembly, and using an overflow tailings slurry output by the magnetic separator directly to the feedbox to mix with the raw coal feed received at the feedbox.
In one form of the inventive method, the magnetic separator includes an overflow weir outputting the overflow tailings slurry. The overflow weir is integrally formed with the feedbox such that the overflow tailings slurry output at the overflow weir consists of a wall of water which mixes with the raw coal feed received by the feedbox.
It is the object of the present invention to:
improve the mixing of a raw coal feed received at a coal preparation plant with water;
provide an apparatus for use in coal preparation plants occupying minimal space; and
more efficiently operate a coal preparation plant.
Other objects, aspects and advantages of the present invention can be obtained from a study of the specification, the drawings, the appended claims.